Castor



FIG. 1 is a front, left perspective view of a castor showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a left side view, the opposite side view being a mirror image thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof. 

We claim the ornamental design for a castor, as shown and described. 